Inlet air heating system for a gas turbine engine

ABSTRACT

A gas turbine engine has an inlet for delivering air into a compressor section. The compressor section is connected to feed air into a combustion section, wherein the air mixes with fuel and combusts. The combustion section is connected to turbine rotors such that products of combustion can pass over the turbine rotors to drive the turbine rotors. An exhaust communicates with the turbine sections to receive the products of combustion. A bleed tap communicates the exhaust to the inlet. A control controls the amount of exhaust gasses tapped into the inlet to achieve desired operating conditions.

BACKGROUND OF THE INVENTION

The present invention relates generally to gas turbine engines and more particularly to an inlet air heating system of the engine and method of operating the same.

Gas turbine engines are known, and typically include an inlet through which air passes to a compressor section. The air is compressed in the compressor section and passed downstream into a combustion section. In the combustion section, air is mixed with fuel and burned. Products of this combustion pass downstream across turbine rotors, to drive the rotors. A good deal of control is included in modern gas turbine engines.

One recent advancement in gas turbine engines is the so-called dry low NOx or “DLN” combustion systems. These are often utilized in industrial gas turbine engines to achieve very low levels of NOx emissions, without any need for water injection. These engines typically have a very narrow operating range over which emissions are kept low.

One way to increase the operating range is a concept known as inlet bleed heat. Inlet bleed heat involves bleeding off compressor discharge air and injecting it into the inlet air passing into the gas turbine engine. This heat increases inlet air temperature and reduces the power provided by the gas turbine engine. The use of the bleed air reduces the power in that as the inlet temperature increases, the provided power decreases. Unfortunately, bleeding off compressor discharge air reduces engine efficiency.

SUMMARY OF THE INVENTION

A gas turbine engine has an inlet for delivering air into a compressor section. The compressor section is connected to feed air into a combustion section, where the air mixes with fuel and combusts. The combustion section is connected to turbine rotors such that products of combustion can pass over the turbine rotors to drive the turbine rotors. An exhaust communicates with the turbine sections to receive the products of combustion. A bleed tap communicates the exhaust to the inlet. A control controls the amount of exhaust gasses tapped into the inlet to achieve desired operating conditions without a loss in engine efficiency. Also, an inventive method and a system for reducing the power from a gas turbine engine are claimed.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a gas turbine engine incorporating a unique inlet air heating system.

FIG. 2 shows a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A gas turbine engine 20 is illustrated in FIG. 1. An inlet 22 delivers air to a low pressure compressor section 24, and downstream to a high pressure compressor section 26. Air from the compressor section 26 passes into a combustion section 27, and is mixed with fuel and burned. Preferably, the combustion section 27 is of a dry low NOx premix (DLN) type wherein fuel and air are premixed prior to combustion to assure flame temperatures are kept uniformly low to prevent formation of NOx. Products of this combustion pass over a high pressure turbine 28, and a low pressure turbine 30, driving the turbine rotors 128 and 130. The turbine rotors in turn drive compressor rotor 126 and compressor rotor 124, respectively. Downstream of the turbine sections the products of combustion pass into an exhaust 32. As shown, a tap line 34 taps a portion of the exhaust gas through a blower 36, and into a tap line 38. The tap line 38 bleeds gas into inlet 22 in controlled amounts. Although no fan section is shown, the present invention also extends to engines including a fan located upstream of the compressor sections 26, 24.

The amount of gas bled into the inlet 22 is controlled to achieve a desired amount of power to be delivered from the turbine sections 28 and 30. As shown schematically in FIG. 1, the turbine sections 28 and 30 deliver power to a generator 40.

In some applications, if the pressure difference between the exhaust 32 and the inlet 22 is sufficient, blower 36 may not be necessary. As an example, if a heat recovery steam boiler is included, the pressure difference might be sufficient. Instead, a simple damper 42, as shown schematically in FIG. 2, may be sufficient. As should be appreciated, the damper is rotated under the control of a motor 44 to control the amount of air delivered from exhaust 32 to inlet 22.

Notably, the exhaust gasses may have corrosive materials produced when burning fuel. Thus, with this system bleeding air from the exhaust through the lines 34, 38, the material and coatings of the turbine sections 28 and 30, and even perhaps the compressor sections 24 and 26, should be selected to resist any potential corrosion issues.

By recirculating gas from the exhaust 32 to the inlet 22, the temperature of the inlet air can be increased, and the oxygen content reduced. Reducing the oxygen content may further reduce NOx emissions.

A worker of ordinary skill in this art would recognize how much air to deliver from the exhaust 32 to the inlet 22 dependent upon the relative temperatures at the two locations preferably measured by sensor 39 and sensor 41, respectively. Sensors 39, 41 send signals to a control 43 for the blower motor 36, or the damper motor 44. Control 43 can be any appropriate processor. Dependent on the desired temperature, and operating temperature, the air delivered to the compressor 24 can be between zero and twenty percent exhaust gas.

Also, the tap lines 34 and 38, along with the blower motor 36, or damper 42, can be connected to existing gas turbine engines.

Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention. 

1. A gas turbine engine comprising: an inlet for delivering air into a compressor section; the compressor section connected to feed air into a combustion section, wherein the air mixes with fuel and combusts, and the combustion section connected to a turbine section such that products of combustion can pass over a turbine rotor in the turbine section to drive the turbine rotor; an exhaust for communicating with the turbine section to receive the products of combustion; and a tap communicating said exhaust to said inlet, and a control for controlling an amount of exhaust gas tapped into the inlet to achieve desired operating conditions.
 2. The gas turbine engine as set forth in claim 1, wherein the amount of gas tapped from the exhaust to the inlet is controlled to achieve a desired inlet temperature at the inlet.
 3. The gas turbine engine as set forth in claim 2, wherein temperature sensors sense the temperature at the inlet and the exhaust and send signals to the control.
 4. The gas turbine engine as set forth in claim 1, wherein the control controls a blower to control the amount of exhaust gas passing from the exhaust to the inlet.
 5. The gas turbine engine as set forth in claim 1, wherein the control controls a damper to control the amount of exhaust gas passing from the exhaust to the inlet.
 6. The gas turbine engine as set forth in claim 1, wherein the turbine rotors drive a generator to create electricity.
 7. The gas turbine engine as set forth in claim 1 wherein the combustion section is of a dry low NOx type.
 8. A method of operating a gas turbine engine comprising the steps of: (a) delivering air from an inlet to a compressor section; (b) compressing air and delivering the air into a combustion section, mixing the compressed air with fuel and combusting the mixture, passing products of the combustion over turbine rotors to drive the turbine rotors; (c) receiving the products of combustion at an exhaust; and (d) tapping gas from said exhaust to said inlet, and controlling the amount of gas tapped to the inlet to achieve desired operating conditions in the gas turbine engine.
 9. The method as set forth in claim 8, wherein the amount of tapped gas is controlled to achieve a desired inlet temperature at the inlet;
 10. The method as set forth in claim 8, wherein the turbine rotors drive a generator to create electricity.
 11. A system for controlling the power provided by a gas turbine engine comprising: a tap line to tap exhaust gas from an exhaust of a gas turbine engine, and deliver the tapped exhaust gas to an inlet of the gas turbine engine; and a control for controlling an amount of tapped exhaust gas that is delivered to the inlet of the gas turbine engine to achieve desired operating conditions.
 12. The system as set forth in claim 11, wherein the amount of gas tapped from the exhaust to the inlet is controlled to achieve a desired inlet temperature at the inlet.
 13. The system as set forth in claim 12, wherein temperature sensors sense the temperature at the inlet and the exhaust and send signals to the control.
 14. The system engine as set forth in claim 11, wherein the control controls a blower to control the amount of exhaust gas passing from the exhaust to the inlet.
 15. The system as set forth in claim 11, wherein the control controls a damper to control the amount of exhaust gas passing from the exhaust to the inlet. 